Título en español.

Holstein heifers grazing unrestrictedly at 9 head/ha on steep, intensively managed grass pastures in the humid mountain region, and receiving no concentrate feed, gained 0.59 kg/head daily over a 240 day period. Heifers which received an additional 2.3 kg/head/day of concentrates gained 0.69 kg/head/day, and carrying capacity of the pastures was increased to 12 head/ha. Heifers grazing for only 8 hours/day, and fed 3.6 kg/head/day of concentrates gained 0.75 kg/head/day and carrying capacity of the pastures was increased to 15 head/ha. It was not economically beneficial to increase weight gains or carrying capacity of the pastures by feeding concentrates or by restricting grazing. In a 360-day experiment, during a 90-day period between all-grass rations, heifers ted only on pasture gained 0.58 kg/head/day and those that grazed for 6 hours/day and were fed 2.3 kg/head/day of concentrates made similar gains averaging 0.53 kg/head/day. However, heifers removed from the pastures during this period and fed 6 kg of bulky feed/head/day gained only 0.23 kg/head/day. When all three groups were returned to a full grass ration, those previously fed only on grass averaged 0.46 kg/head/day; those fed on bulky feed during the previous 90 days gained at a similar rate of 0.41 kg/ head/day, but those previously on restricted grazing plus concentrates gained only 0.32 kg/head/day. Overall average gains for the 360-day period were 0.54, 0.43 and 0.49 kg/head/day for these three feeding regimes, respectively. It was more economically beneficial to feed concentrates and to restrict grazing than to put the heifers on a full ration of bulky feed during periods of forage scarcity.En un experimenlo que duró 240 días, novillas Holstein alimentadas sólo con pastos administrados intensivamente en la región montañosa húmeda de Puerto Rico aumentaron de peso a razón de .59 kg/cabeza y día, manteniéndose 9 cabezas por hectárea. Las novillas que además del pasto recibieron 2.3 kg de alimento concentrado por cabeza y día aumentaron .69 kg por cabeza y día manteniéndose 12 cabezas/ha. Las novillas a las cuales se les permitió sólo 8 horas diarias de pastoreo, además de recibir 3.6 kg de alimento concentrada por cabeza y día, aumentaron .75 kg por cabeza y día, manteniéndose 15 cabezas/ha. No resultó económico aumentar las ganancias de peso de las novillas o el número de cabezas que el pasto puede mantener mediante alimentación suplementaria con alimentos concentrados o limitando las horas de pastoreo. En otro experimento, las novillas que se alimentaron só1o con pasto durante un período de 90 días entre 2 períodos en que fueron alimentadas solamente con pasto, aumentaron a razón de .58 kg por cabeza y día. Las novillas que durante ese período de 90 días pastaron durante sólo 6 horas al día, además de recibir 2.3 kg de alimento concentrado por cabeza y día, tuvieron similares aumentos de peso, que en promedio ascendieron a .53 kg por cabeza y día. Sin embargo, las novillas que se retiraron de los pastos durante ese período y se alimentaron con 6 kg de alimento voluminoso (""bulky"') por cabeza y día aumentaron só1o .23 kg por cabeza y día. Cuando todas las novillas volvieron a alimentarse con pasto, las alimentadas previamente con pasto sólo aumentaron .46 kg por cabeza y día, las alimentadas sólo con alimento voluminoso ("bulky") durante los 90 días anteriores aumentaron .41 kg por cabeza y día, pero las que habían sido restringidas a 6 horas de pastoreo además de recibir alimento concentrado aumentaron sólo .32 kg por cabeza y día. Tomado en conjunto, durante los 360 días que duró el experimento las novillas aumentaron a razón de .53, .43 y .49 kg por cabeza y día con estos tres regfmenes alimenticios, respectivamente. Result6 mas econ6mico alimentarlas con alimento concentrado combinado con pastoreo limitado que exclusivamente con alimento voluminoso ("bulky") durante períodos en que el pasto escasea

Disponibilidade e qualidade do capim-elefante com e sem irrigação adubado com nitrogênio e potássio na estação seca Forage yield and quality of elephantgrass response to irrigation and nitrogen and potassium fertilization in the dry season

Objetivou-se com este trabalho avaliar os efeitos da irrigação e da adubação com N e K sobre a disponibilidade e a qualidade da matéria seca em pastagem de capim-elefante cv. Napier adubada com N e K nas dosagens de 100:80; 200:160; 300:240 e 400:320 kg.ha-1.ano-1 de N e K2O, respectivamente, no período seco do ano. Foram conduzidos dois experimentos (área irrigada - AI e não-irrigada - ANI), segundo delineamento de blocos casualizados com três repetições, em que a unidade experimental consistiu de parcelas (piquetes) de 300 m², nas quais foram aplicados os tratamentos. No período de avaliação (maio a setembro/2001 - período seco), as disponibilidades de matéria seca total (DMST) e lâmina foliar (DMSLF) apresentaram valores proporcionais às doses de nitrogênio e potássio. A irrigação teve efeito significativo sobre a DMSLF. No entanto, os teores de FDN e FDA, ao longo do período seco, na área não-irrigada foram menores que na área irrigada. As concentrações de PB e dos macrominerais (P, K, Ca e Mg) não foram influenciadas pelas doses de N e K e pela irrigação, tanto na área irrigada como na não-irrigada.<br>An experiment was carried out in experimental plots of 300 m² in size to evaluate the effects of doses of NK fertilization and irrigation on forage mass yield and quality of elephantgras cv Napier during the dry season. The experimental design was completely randomized with three treatment replications. The experimental treatments were arranged in a 4 x 2 factorial combination of four N-K2O doses with and without irrigation, in the dry season. N-K2O doses were: 100-80; 200-160; 300-240 and 400-320 kg.ha-1, respectively. Figures for total dry forage mass (TDFM), and dry green leaf mass (DGLM) increased in proportion to N-K2O dose from May to September 2001, the dry season period. Irrigation had a marked significant effect on DGLM yield. Leaf samples from irrigated plots had higher contents of neutral and acid detergent fiber as compared to leaf samples from the control plots. Concentrations of crude protein, potash, phosphorus, calcium and magnesium did not respond either to N-K2O doses or to irrigation